In recent years, with the prosperous development in the electronic semiconductor industry, the progress in the process technique and the trends in the market demands, all kinds of electronic devices have been designed to be compact, low-profile and light in weight. However, while the electronic devices have gradually reduced dimensions, they have increasing functions and computing ability. For example, home or business computers, communication chassis, and home or industrial heat exchanger all include many electronic elements that would produce heat during the operation thereof. Among others, electronic chips or elements for executing computation produce the largest part of heat in the computer. Under this circumstance, a heat sink formed from radiating fins and cooling fans for dissipating heat plays an important role in protecting these electronic elements against overheating, so that these electronic elements can maintain at a normal working temperature to fully extend the intended functions thereof.
While the water cooling technique has already been widely applied in personal computers, it is not positively employed in heat exchangers for communication, home or industrial purpose. In the water cooling technique, the large-volume radiating fins are omitted, and heat from heat sources in the electronic system is collected and transferred to the working fluid. Then, the heat-absorbed working fluid exchanges heat with air via a heat exchanger. Since the length of the pipeline for water cooling can be changed according to actual need, the heat exchanger (i.e. the radiating fins) can be flexibly disposed at different positions and can be advantageously designed without spatial restriction. However, a water cooling system requires a pump to drive the working fluid to flow in the pipeline, and a water tank to store sufficient water as the working fluid. That is, the water cooling system is subject to the reliability of the pump, possible leakage in the pipeline, and the like. However, due to the increasing heat produced by the heat-producing elements in the personal computer, the water-cooling heat dissipating technique, though not so perfect for use, is still the best choice in the current market for heat management and control. While the water cooling technique can be well applied to the personal computer that has a relatively large volume and is not subject to any spatial restriction, the water cooling technique for heat dissipation seems useless at all in terms of the communication chassis and home or industrial heat exchangers that are usually compact, low-profile and small in volume. Therefore, for the present, heat pipes or small-size heat sinks are still used in the communication chassis and home or industrial heat exchangers for heat transfer, and radiating fins are further used to exchange heat with ambient air. In view of these problems, the information industry and other related electronic industries all have positively tried to find other heat dissipation techniques capable of providing higher heat flux, so as to meet the growing demands for heat dissipation.
In the conventional heat dissipation techniques, heat pipe and uniform temperature plate are also used as heat transfer elements. In manufacturing the heat pipe and the uniform temperature plate, a sintered layer is formed on the inner wall surface thereof to serve as a wick structure. To form the sintered layer, first fill copper particles or powder in the inner wall of the heat pipe and the uniform temperature plate, and then tightly press the metal (i.e. copper) particles or powder before sintering the metal particles or powder in a sinter furnace to form a porous wick structure. While the sintered layer provides a capillary force, it also increases an overall thickness of the heat pipe and the uniform temperature plate, preventing the latter from being effectively slimmed. As to the currently known vapor chamber (VC), it uses a sintered core, grids, or grooves to produce the capillary force for driving steam-water circulation in the heat pipe or the vapor chamber. However, the above structure is not ideal for use because it involves in a very complicated manufacturing process and accordingly, increased manufacturing cost.
It is also possible to use the conventional loop type thermosiphon device as a heat transfer element. Since the conventional loop type thermosiphon device mainly employs capillary force and gravity force to drive steam-water circulation, it is subject to the limitation by gravity force. Further, the loop type thermosiphon device has a relatively higher thermal resistance, and can only have a restricted rolling angle. That is, there is a lot of limitation in the design and application of the conventional loop type thermosiphon device.
Therefore, the currently commercially available all-in-one personal computers or remote radio units (RRU) all adopt the so-called heatpipe cooler solution. However, the heat pipe has limitation in its heat load, and accordingly, multiple pieces of heat pipes are frequently required to inevitably increase the cost of the personal computer and the RRU. Meanwhile, the heat pipe may not necessarily have a thermal resistance that always satisfies the thermal resistance requirement for a central processing unit (CPU).
Moreover, the selection of a vapor core is not easy. It is very important to select a proper vapor core, which must be able to keep the condensate at a desired flowing speed and must be able to maintain sufficient capillary pressure to overcome any undesired influence from the force of gravity on the vapor and the condensate.
In brief, the prior art heat pipe or vapor chamber has the following disadvantages: (1) uneasy to fabricate; (2) unable to be slimmed; (3) high manufacturing cost; and (4) consuming time and labor to manufacture.